Glutamate is the major excitatory neurotransmitter in the mammalian brain, and is packaged into secretory vesicles for exocytotic release by a family of vesicular transporters (VGLUT1-3). Surprisingly, VGLUT3 is expressed in discreet populations of neurons better known for their release of other classical transmitters: dopamine, serotonin GABA and ACh. I aim to determine the precise cellular and subcellular location of VGLUT3 in monoamine and cholinergic neurons, focusing in particular on the relationship of the carrier to sites of synaptic release and to vesicles that contain monoamines or ACh. A second aim is to evaluate the role of VGLUT3 in glutamate release. To achieve this, I will examine the location of VGLUT3 in the brains of mice that express a fluorescent reporter in only monoamine neurons by light and electron microscopy, as well as to produce and examine VGLUT3 knockout mice that express a fluorescent reporter under the control of the VGLUT3 promoter. These mice will be used for immunostaining and for electrophysiological recordings. These findings will help us to better understand the physiological role of VGLUT3 in monoamine neurons, as well as to explore the impact of VGLUT3 expression on these signaling pathways and ultimately on behaviors that are affected by monoamine neurons, such as motor control, affect, reward and drug addiction. [unreadable] [unreadable]